/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformAtomics.h
Generic implementation...you are required to implement at leastFPlatformAtomics::InterlockedCompareExchangebut they are listed here to provide a base implementation in terms ofFPlatformAtomics::InterlockedCompareExchangeand easy copy-paste
struct FGenericPlatformAtomics